Web page change monitor/notifier

Hello,
I'm looking for (preferably) freeware which notifies you when a certain web page has changed from a web site you want to follow up closely. It should also be able to detect changes from parts like the Star Posts section over here, or the CEO Updates section of a company's PHP forum.
Any suggestions or experiences would be very welcome!
Hasse

ps Sorry for not providing much more information... I had written a more elaborate post with some possibly interesting google search results & examples, links to specific freeware lists etc, which could provide some more 'food' for thought, but some stupid key stroke made it vanish...